Manufacture of methylamines

ABSTRACT

Methylamines are synthesized by ammonolysis of methanol at elevated temperature and pressure and in the presence of hydrogen which suppresses formation of undesirable corrosion-inducing compounds.

United States Patent [191 Nichol] 1March 13, 1973 MANUFACTURE OFMETHYLAMINES 21 Appl. No.: 79,771

[30] Foreign Application Priority Date Nov. 3, 1969 Great Britain..53,695/69 [52] US. Cl ..260/583 J, 260/583 R, 260/585 B [51] Int. Cl..C07c 85/06 [58] Field of Search ..260/583 R, 585 B, 583 J [56] 1References Cited UNITED STATES PATENTS 2,365,721 12/1944 Olin et al...260/585 B 5/1939 Covert ..260/585 B X 9/1936 Guinot ..260/585 BPrimary Examiner-Lewis Gotts Assistant Examiner-Richard L. RaymondAttorney-Cushman, Darby & Cushman [57] ABSTRACT Methylamines aresynthesized by ammonolysis of methanol at elevated temperature andpressure and in the presence of hydrogen which suppresses formation ofundesirable corrosion-inducing compounds 7 Claims, 1 Drawing FigureMANUFACTURE OF METHYLAMINES The present invention relates to themanufacture of methylamines.

Alkylamines are widely manufactured and several processes are known fortheir manufacture. For example, an alkyl halide can be ammonolysed insolvent ether to produce the corresponding hydrohalide salts which arethen decomposed to give a mixture of primary, secondary and tertiaryalkyl amines. Aldehydes and ketones may also be ammonolysed in thepresence of hydrogen and a catalyst such as cobalt ornickel to give amixture containing mostly primary, secondary, and tertiary alkyl amines.Another method of manufacture, is the ammonolysis of an alcohol in thevapor phase in the presence of a catalyst which may be either adehydration catalyst, such as alumina, or a hydrogenation catalyst suchas nickel-aluminum or a copper-aluminum mixture. In ammonolysisprocesses for the production of ethylamines and higher amines it isfound that nitriles are easily formed and therefore the reaction may beconducted in the presence of molecular hydrogen to suppress nitrileformation. Nitriles are not formed however when methylamines areproduced by the ammonolysis of methanol and it is not therefore thepractice to have molecular hydrogen present in this type of methylaminessynthesis. Thus one process for the manufacture of methylamines consistsin passing ammonia methanol and, preferably, recycled mono-, diandtrimethylamines over a dehydration catalyst, for example silica-alumina,at elevated temperature, for example in the range 400 to 450C and atelevated pressure, for example in the range 150 p.s.i.g. to 300 p.s.i.g.

We have found that during passage of the methanol, ammonia and, ifdesired, recycled methylamines over the catalyst, some of the methanolis oxidized to formaldehyde. Furthermore, we have found that subsequentreaction between the formaldehyde and dimethylamine leads to formationof N,N,N, N,- tetramethyldiaminomethane (BDM). The formation offormaldehyde and BDM accounts for approximately 0.4 percent by weight ofthe methanol used in this process; this is a significant wastage ofmethanol. Of more importance, however, is our discovery that BDM is acause of severe corrosion in the plant used for the process. We havefound that as little as w/w of BDM in aqueous methylamine solutionscauses severe corrosion. We have now found means whereby the formationof formaldehyde and BDM with their consequent disadvantages may besuppressed.

According to the present invention, a process for manufacturingmethylamines comprises ammonolysis of methanol in the vapor phase at anelevated temperature and pressure in the presence of molecular hydrogen.

By ammonolysis we mean replacement of one or more hydrogen atomsattached to a nitrogen atom in ammonia or methylamines by one or moremethyl groups from methanol with the formation of one or more moleculesof water.

Ammonolysis is suitably carried out using ammonia and/or methylamines.Preferably both ammonia and methylamines are used, the amines beingrecycled from a later stage in the process.

Preferably the molar ratio of ammonia and/or amines to methanol usedlies in the range 1.5 to l to 8 to Land advantageously is about 4 to l.

A suitable temperature of operation of the process lies in the range 350to 500C, preferably in the range 400 to 450C. The process isadvantageously operated at elevated pressure, suitably within the rangep.s.i.g. to 500 p.s.i.g, preferably 200 p.s.i.g. to 300 p.s.i.g.

The process is preferably operated catalytically, suitable catalystsbeing dehydration catalysts, for example alumina, silica/alumina, thoriaand bauxite.

Advantageously, ammonia and hydrogen are present in an approximatelyequimolar ratio.

The invention will now be further described by way of example withreference to the accompanying drawing which is a simplified flow diagramof the process.

Methanol is mixed with ammonia from an outside source, and with recycledammonia and methylamines from line 1. The mixed stream is fed to avaporizer 2 and after vaporization it is mixed with hydrogen. Thehydrogen is supplied either wholly or in part from an outside sourcealong line 3, the remainder being hydrogen recycled along line 3 fromthe synthesis of the methylamines.

The combined feed is then fed to a superheater 4, a heat exchanger 5, apreheater 6 and thence to the methylamines synthesis reactor 7containing a dehydration catalyst which operates at a temperature ofabout 425C and a pressure of about 250 p.s.i.g.

After reaction, the process stream is cooled initially in heat exchanger5 and then in cooler 8 to about 100C. Residual hydrogen and a littleammonia are flashed off in flash drum 9 and recycled along line 3.Additional fresh hydrogen is added as necessary into line 3.

The remaining ammonia, methylamines and water formed in the reaction isfed to the ammonia column 10, which is operated at a pressure of about250 p.s.i.g. Ammonia and some trimethylamine are separated from theproduct, the trimethylamine forming an azeotrope with ammonia, and thisis recycled to the synthesis reactor 7 through line 1. The product fromthe ammonia column passes to the trimethylamine column 11, which isoperated at about 150 p.s.i.g. and in which trimethylamine is separatedfrom the product stream by an extractive distillation process withwater. The trimethylamine obtained may be wholly or partially recycledthrough line 1 or fed to storage along 1ine12. The remaining productstream passes to the dehydration column 13 which is operated at aboutp.s.i.g. and in which water is separated from monoand dimethylamine. Themixture of amines passes from the dehydration column 13 to thedistillation column 14 which operates at about 100 p.s.i.g. and in whichmonomethylamine is separated from dimethylamine. The monomethylamine maybe wholly or partly recycled through line 1 or it may be passed tostorage along line 15. The dimethylamine may be wholly or partlyrecycled through line 1, or it may be passed to storage along line 16.

We have found that when hydrogen is absent from the process corrosionoccurs in the plant, in particular in the trimethylamine column 11 andin the dehydration column 13.

The use of hydrogen in the process reduces the amount of BDM andformaldehyde formed, and thus reduces both the wastage of methanol andthe corrosion of the plant.

lclaim:

1. In a process for the production of methylamines by the ammonolysis ofmethanol in the vapor phase at elevated temperature and pressure, theimprovement whereby (a) loss of methanol by the formation of undesiredformaldehyde and (b) corrosion resulting from the conversion of saidformaldehyde to N,N,N',N'- tetra-methyl diaminomethane are avoided, saidimprovement comprising carrying out said ammonolysis in the presence ofmolecular hydrogen in amount sufficient to suppress the formation ofsaid formaldehyde and N,N,N',N'-tetra-methyl diaminomethane.

2. A process as claimed in claim 1 wherein ammonolysis is carried outusing both ammonia and methylamines.

the range 1.5 to l to 8 to l.

4. A process as claimed in claim 1 wherein the temperature used lies inthe range 350 to 500C and the pressure used lies in the range 100 to 500p.s.i.g.

5. A process as claimed in claim 1 wherein the process is operated inthe presence of a catalyst selected from the group consisting ofalumina, silica/alumina, thoria and bauxite.

6. A process as claimed in claim 1 wherein ammonia and hydrogen arepresent in an approximately equimolar ratio.

7. A process as claimed in claim 1 which comprises ammonolysis ofmethanol in the vapor phase at a temperature in the range 400 to 450Cand a pressure in the range 200 to 300 p.s.i.g. over a silica-aluminacatalyst and in the presence of molecular hydrogen, wherein the molarratio of ammonia and/or amines to methanol used is about 4 to l and theammonia and 3. A process as claimed in claim 1 wherein the molarhydrogen are Present in about equimolar proportions

1. In a process for the production of methylamines by the ammonolysis ofmethanol in the vapor phase at elevated temperature and pressure, theimprovement whereby (a) loss of methanol by the formation of undesiredformaldehyde and (b) corrosion resulting from the conversion of saidformaldehyde to N,N,N'',N''-tetra-methyl diaminomethane are avoided,said improvement comprising carrying out said ammonolysis in thepresence of molecular hydrogen in amount sufficient to suppress theformation of said formaldehyde and N,N,N'',N''-tetra-methyldiaminomethane.
 2. A process as claimed in claim 1 wherein ammonolysisis carried out using both amMonia and methylamines.
 3. A process asclaimed in claim 1 wherein the molar ratio of ammonia and/or amines tomethanol used is in the range 1.5 to 1 to 8 to
 1. 4. A process asclaimed in claim 1 wherein the temperature used lies in the range 350*to 500*C and the pressure used lies in the range 100 to 500 p.s.i.g. 5.A process as claimed in claim 1 wherein the process is operated in thepresence of a catalyst selected from the group consisting of alumina,silica/alumina, thoria and bauxite.
 6. A process as claimed in claim 1wherein ammonia and hydrogen are present in an approximately equimolarratio.